Method of improving surfaces of aluminium



To aZZ whom it may concern:

Be itknown that I, ARTHUR V. DAvIs, of Pittsburg, in the county of Allegheny and State of Pennsylvania, have invented a new i i 5 and useful Improvement in Methods of Im- 11 proving Surfaces of Aluminium,of which the tion. A

I I have discovered that by treating the aluminum with a combination of hydrofl lm'ic acid alg d nitrig acid, its surface appearance da'fibe greatly improved, and the dullness of the metal removed so as to enhance its value in the arts. Neither hydrofluoric acid alone nor nitric acid alone will afiord the desired I I result satisfactorily, but by a mixture of them, or by their conjoint and successive use,

excellent results are obtained.

7 To determine the proper proportions of 20 hydrofluoric acid of any given commercial strength to be added to the concentrated nitric acidof commerce in order to prepare a desirable mixture for my purpose, I may proceed as followsz-Nitric acid of commerce 2 5 having specific gravity of about 31.4: Baum i'spreferably diluted with, say, about one to twenty parts of water. The proportion of wa- Q ter used is variable according to the temperature of the mixture of acids ultimately employed for treating the aluminum, for when I the mixture is to be used hot a less proportion of acid will answer, than when the mixture is cold. A good working test of the pro- ME'THQD or IMPROVING SURFACES OF ALummlumi SPECIFICATION forming part of Letters Patent No. 528,513, dated October 30, 1 894.

Application filed January 24, 1894- Berlal Ila 497,912. (No specimens-) following is a full, clear, and exact descripportion of hydrofluoric acid to be added to the PATENT OFFICE.

ARTHUR. v. DAVIS,- or PITTSBURG, PENNSYLVANIA.

nitric acid is to place in the dilute nitric acid a piece of aluminum, and to add hydrofluoric acid until gas is evolved freely from the surface of the aluminum. Such evolution of gas will indicate that theacids have been combined properly. Having ascertained the proper proportions (which are, of course, variable because of the uncertain strength of the hydrofluoric acid of commerce, and variable also according'to the temperature of the mixture for a hot solution of the acid may be used when more 1 u e than a cold solution),

the aluminum to be treated is immersed therein and is allgweimomainuntititssur face heco n es bright. It is then removed and washed, prefefably'with hot water, and havoperation is complete.

I do not limit myself to the use of the acids in any given proportion, nor do I disclaim the addition of other materials or steps in the practice of my process; but I What I claim is--- a The method of improving the surface appearance of aluminum, which consists in treating the surface with a mixture of h 6gpfluoric and and nitric acid, substantla y as M; uh-W m "a I s I ing been dried by sawdust or otherwise, the 1 In testimony whereof I have hereunto set W, B. Coawm. 

